1. Field of the Invention
The present invention relates to a substrate using a monocrystal material. More particularly, the present invention relates to a substrate using a monocrystal substrate the surface of which is thermally oxidized, a liquid jet recording head substrate using the foregoing substrate, a method of manufacture of such a substrate, a liquid jet recording head using such a substrate, and a recording head provided with such a recording head.
2. Related Background Art
Of the ink jet recording methods which can be used for various printers, copying machines, facsimile apparatuses, and others, a liquid jet recording method wherein recording liquid is thermally activated to fly it for the recording performance is the recording method which has attracted a particular interest in the art recently because compared to the impact printer and other recording methods, it is capable of performing recording with a lesser noise yet at a high speed. Moreover, with this method, it is possible to achieve a highly precise recording of a higher image quality by the use of a compact recording apparatus.
A liquid jet recording head using such a liquid recording method is, for example, structured as shown in FIGS. 5A and 5B that on a supporting member 1, exothermic resistive members 2a are arranged as thermal energy generating elements to generate the thermal energy to activate liquid to form a substrate 8, and in the positions corresponding to the exothermic resistive members 2a thereon, there are formed liquid passages 6 conductively connected to the discharging ports (orifices) 7 to eject liquid, and a liquid chamber 10 which supplies liquid to the foregoing passages. In FIGS. 5A and 5B, a numeral 5 designates a ceiling board and 9, a liquid supply inlet.
Also, as shown in FIGS. 6A and 6B, at least an electrode layer 3 and an exothermic resistive layer 2 are laminated on the supporting member 1. The substrate 8 is thus obtained by forming the exothermic resistive members 2a electrically connected to the pairs of electrodes 3a and 3b provided at given intervals in a given configuration produced by patterning these layers.
In this respect, on the substrate 8 having the electrodes 3a and 3b as well as the exothermic resistive members 2a, a protective layer 4 and various other upper layers are provided as required.
As a supporting member 1 utilized for the formation of the substrate 8 for a liquid jet recording head structured such as this, a board type silicon, glass, or ceramics, or the like has hitherto been used.
Of these materials, silicon is often used for the substrate for the reasons given below.
In a case of a recording head structured on a substrate using a glass supporting member, an excessive heat accumulation takes place in the supporting member when the driving frequency of the exothermic resistive member is increased because of the inferior heat conductivity of the glass supporting member. As a result, liquid in the recording head is unnecessarily heated to contain bubbles. There is then a possibility that a disabled liquid ejection or the like occurs inevitably.
In a case of a ceramic supporting member, an alumina member is often used because compared to glass, it has a better conductivity, at the same time enabling the production of a substrate in a comparatively large size. However, since the alumina supporting member is produced by baking the powdered material, there tends to occur surface defectives such as pin holes or extrusions of several .mu.m to several ten .mu.m on the surface of the supporting member. Accordingly, when wiring and other patterning are conducted on this supporting member, defectives such as wiring opens or shorts with such defectives as its starting points take place, leading to the yield reduction. Also, the surface roughness of the ceramic supporting member is usually Ra=approximately 0.15. It is often difficult to obtain an optimal smoothness required to form the deposited layer of a desirable durability for the electrothermal transducers and the like. Therefore, in the case of a recording head structured on the alumina supporting member, there is a possibility that the electrothermal transducers and others on the alumina supporting member which generates heat repeatedly are peeled or affected in some other ways; thus leading to a shorter durability in some cases.
There is of course means to improve the close contact between the supporting member and the electrothermal transducers and other by polishing the surface to increase the smoothness thereof. However, there is automatically a limit for the adjustment of the surface roughness because alumina is a highly hard material.
Also, an alumina grazed supporting member which is an alumina supporting member on which a greasing layer is provided enables the solution of the problem such as the presence of the pin holes, extrusions or other surface defectives as well as the surface roughness. However, the grazing layer cannot be formed in a thickness of less than 40 to 50 .mu.m due to its method of manufacture. Consequently, there is a possibility as in the glass supporting member that an excessive heat accumulation takes place.
On the other hand, in a case where silicon supporting member 1 is used, there is no problem of the excessive heat accumulation such as encountered in the cases of the glass and ceramic supporting members 1. Particularly, when monocrystal silicon wafers are used, there is almost no possibility that the breakage of wiring and others as described above will take place because its surface condition is highly desirable. Therefore, as disclosed in Japanese Patent Laid-Open Application No. 2-125741, for example, the monocrystal silicon wafer is used for the supporting member for the above-mentioned liquid jet recording head which utilizes thermal energy.
Now, in recent years, there is an increasing desire to provide as early as possible a recording apparatus capable of performing recordings of a better image quality at a higher speed in the field of recording in which the liquid jet recording methods are employed. From with a view to meeting such demands on the high-speed recording, the research and development have been made assiduously to make available a large recording head, the so-called full line head, to perform recordings on a wide recording medium.
As a result of such research and development, it is found that although the monocrystal silicon wafer is best suited for the foregoing recording head supporting member as far as the recording head can be comparatively small, there are problems yet to be solved in order to make the monocrystal silicon wafer usable as a supporting member for a large recording head because the drawbacks given below will ensue when it is used as the supporting member for a large recording head.
In other words, for a liquid jet recording head, a heat storage layer (lower layer) is provided in a thickness of 0.3 to 10 .mu.m in order to obtain a desirable balance between the capabilities of heat accumulation and release for a better transfer of heat to the recording liquid. In this case, the aforesaid substrate is fabricated in such a manner that a heat accumulation layer of SiO.sub.2 layer is formed by thermally oxidizing the surface of the monocrystal silicon wafer cut out from the monocrystal ingot, and then subsequent to having formed the foregoing exothermic resistive layer, wirings, and the like, it is cut per recording head.
However, according to the researches and experiments by the present inventor et al with a view to obtaining a large recording head, there is found a problem that substrates 1a and 1b cut out from the end portion of a monocrystal silicon are curved like a bow as shown in FIG. 1, respectively. Then, the maximum amount of such a deformation is as much as 60 to 90 .mu.m, and the substrate is often broken if the deformation is forcibly corrected. Also, even when such a deformation is small, it becomes difficult to conduct its grinding machining properly after the cutting process, the accuracy of patterning becomes incorrect when the wirings are patterned on the supporting member, or the wirings arranged on the substrate can hardly be connected electrically to IC and others precisely among other problems thus found. It is also found that a liquid jet recording head which is fabricated with a curved substrate causes recording liquid to be displaced on a recording medium, leading to the missing or uneven recording dots to lower the quality of the recorded images. Also, if this portion where such a deformation takes place, that is, the end portion of a silicon wafer, is not used for the recording head substrate, it is found that the fabrication cost of the substrate itself becomes extremely high.
In order to avoid this, it is attempted to form the heat accumulation layer by the application of some other methods than the thermal oxidation, such as a vacuum film deposition (sputtering, thermal CVD, plasma CVD, ion beam, or the like). The result are, however, that the heat accumulation layer has an uneven distribution of film thickness, the film deposition speed become slower, or dust particles tend to be generated-during the film deposition. These dust particles are mixed in the film to often create granular defectives of several .mu.m in size. When this type of defectives is present, the exothermic resistive members formed on such defectives tend to be broken by cavitation in durable ejection. In addition, there is a fear that if the supporting member is conductive, electric current leaks from the defective portions to cause a short circuit electrically.
As still another method to form the heat accumulation layer, a spin-on-glass or dip-and-pickup method may be used to perform silica coating. However, none of them presents a desirable film quality for the purpose. There is also a problem that the dust particles are mixed when the film is being coated.
As described above, the causes of the substrate deformation are constantly studied. As a result, it, is found that such a curving deformation as this is not recognized on the portions of the substrate where no thermal oxidation layer is formed as the heat accumulation layer, and that the above-mentioned deformation is caused by the thermal oxidation processing. Then, it is further found that the occurrence of the foregoing deformations is due to the fact that the end portions of the wafer, particularly, four corners, are cooled most quickly when cooled after the thermal treatment is given to the monocrystal silicon wafer, and thus, as indicated by arrows in FIG. 2A, tensile stresses are generated along the outer periphery of the supporting member. Accordingly, in a state indicated by the marks+in FIG. 2B, the stresses are distributed in the supporting member to cause the generation of the plastic deformations; hence resulting in the dislocation. When the supporting member is formed by cutting a part of the wafer thus prepared as shown in FIG. 1, the resilient deformations which are present surrounding such dislocations are partly released to allow the deformations to take place.
Therefore, when the monocrystal silicon supporting member is used as a supporting member for a recording head substrate, there is automatically a limit in attaining the elongation of the substrate for the purpose. Consequently, it is required to combine short substrates for a recording head to integrate them for the provision of an elongated head for the achievement of a high speed recording. In this case, however, it is extremely difficult to adjust the junctions between such substrates so that no adverse effect will be produced on an image to be recorded.
Under such circumstances, there has been an increasing desire to make available at a low cost a liquid jet recording head substrate the configuration of which is not restricted by its fabrication processing, and is also capable of easily attaining a high-speed and high-quality recordings without any problems such as the deformation of the recording head substrate associated with its size when it is made larger.